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<div class="sect2" lang="en" xml:lang="en">
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<div>
<h3 class="title"><a id="gimp-tool-curves"></a>5.7. Curves Tool</h3>
</div>
</div>
</div>
<div class="mediaobject">
<img src="../images/toolbox/tools-curves.png" />
</div>
<p>
The Curves tool is the most sophisticated tool used to adjust the
tonality of images.
</p>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3330216"></a>Activate Tool</h4>
</div>
</div>
</div>
<p>
The Curves Tool can be called in the following
order, from the image-menu:
<span class="guimenuitem"><span class="accel">T</span>ools</span>/
<span class="guimenuitem"><span class="accel">C</span>olor
Tools</span>/<span class="guimenuitem"><span class="accel">C</span>urves
.</span>
</p>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3330460"></a>Adjust Color Curves</h4>
</div>
</div>
</div>
<div class="variablelist">
<dl>
<dt>
<span class="term">Channel</span>
</dt>
<dd>
<p>
There are five options: Value for luminosity and contrast; Red,
Green, and Blue for saturation; and Alpha.
</p>
</dd>
<dt>
<span class="term">Reset Channel</span>
</dt>
<dd>
<p>
This button deletes all changes made to the selected channel.
</p>
</dd>
<dt>
<span class="term">Linear and Logarithmic buttons</span>
</dt>
<dd>
<p>
These buttons allow to choose the Linear or Logarithmic type of
the curve. You can also use the same options in Tool Options
dialog.
</p>
</dd>
<dt>
<span class="term">Main Editing Area</span>
</dt>
<dd>
<p>
<span class="guilabel">Input and Output Value Domains</span>: The
horizontal bar (x-axis) represents input values (they are value
levels from 0 to 255). The vertical bar (y-axis) is only a scale
for output colors of the selected channel.
</p>
<p>
<span class="guilabel">The control curve</span> is drawn on a grid and
goes from bottom left corner to top right corner. Pointer x/y
position is permanently displayed in top left part of the grid.
If you click on the curve, a <span class="guilabel">Control point</span>
is created. You can move it to bend the curve. If you click
outside of the curve, a control point is also created, and the
curve includes it automatically.
</p>
<p>
So, each point of the curve represents an 'x' level,
corresponding to an 'y' color. If, for example, you move a curve
segment to the right, i.e to highlights, you can see that these
highlights are corresponding to darker output tones and that
image pixels corresponding to this curve segment will go darker.
With color channels, moving right will decrease saturation ans
can reach the complementary color.
</p>
<p>
To delete all control points (apart from both ends), click on the
'Initialize Channel' button. To delete only one point, move it
onto another point or to grid border.
</p>
</dd>
<dt>
<span class="term">All Channels</span>
</dt>
<dd>
<p>
<span class="guilabel">Load</span>: This button allows you to select a file
holding curve settings.
</p>
<p>
<span class="guilabel">Save</span>: Allows you to save any curves you have set
to a file that can be loaded later.
</p>
</dd>
<dt>
<span class="term">Curve Type</span>
</dt>
<dd>
<p>
<span class="guilabel">Smooth</span>: This mode constrains the curve type
to a smooth line with tension. It provides a more realistic
render than the following.
</p>
<p>
<span class="guilabel">Free</span>: You can draw your curve free-hand with
the mouse. With curve segments scattered all over the grid,
result will be surprising, but poorly repeatable.
</p>
</dd>
<dt>
<span class="term">Preview</span>
</dt>
<dd>
<p>
The Preview button makes all changes to the levels dynamically so
that the new level settings can be viewed immediately.
</p>
</dd>
</dl>
</div>
<div class="variablelist">
<p class="title">
<b>Tool Options dialog</b>
</p>
<dl>
<dt>
<span class="term">Histogram Scale</span>
</dt>
<dd>
<p>
See Linear and Logarithmic buttons in Adjust Color Curves dialog.
</p>
</dd>
<dt>
<span class="term">Sample Average</span>
</dt>
<dd>
<p>
FIXME
</p>
</dd>
</dl>
</div>
</div>
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